Spectroscopic signatures of unconventional superconductivity in twisted trilayer graphene - Part 2*

Magic-angle twisted trilayer graphene (MATTG) has emerged as a novel moiré material that exhibits strong electronic correlations and unconventional superconductivity. We performed high-resolution scanning tunneling microscopy/spectroscopy measurements on MATTG which establish symmetry-breaking cascade and doping-dependent band deformations analogous to magic angle bilayers. Strikingly, upon doping two to three holes per moiré site we observed a pronounced gap accompanied with coherence peak that disappears with increased temperature and magnetic field, indicative of unconventional superconductivity in this system. The observed evolution of tunneling spectrum with doping shows the transition from the U- to V-shaped gap, which is theoretically compatible with a sharp transition from a Bardeen-Cooper-Schrieffer (BCS) to a Bose-Einstein-condensation (BEC) superconductor with a nodal order parameter. We also observed dip-hump structure signaling strongly coupled bosonic mode to the superconductor. Our results pave the way to a deeper understanding of what drives superconductivity in moiré materials.